The present invention relates to the fabrication of integrated circuits in general, and more particularly, to methods of fabricating capacitors in integrated circuits.
Ta2O5 layers having a high dielectric constant have been studied for use as a next generation dielectric in capacitors included in dynamic random access memories (DRAM) having a capacity of 1 Gigabit or more. It may be desirable for the Ta2O5 layers to have improved leakage current characteristics as well as improved heat resistance.
In general, Ta2O5 layers can be formed using thermal chemical vapor deposition (CVD) with Ta(OC2H5)5 and O2 as source gases. These source gases may introduce impurities, such as carbon (C) or water, in the Ta2O5 layer which may increase the leakage current of the Ta2O5 layer. Furthermore, the leakage current may be further increased if the Ta2O5 layer stays in an amorphous state after formation.
A conventional method of reducing the leakage current in a Ta2O5 layer and improving the properties of the layer can include the steps of forming the Ta2O5 layer; curing the Ta2O5 layer by supplementing a deficiency of oxygen in the Ta2O5 layer using a low temperature oxidation annealing process; and crystallizing the Ta2O5 layer by high temperature heating in an oxygen atmosphere and removing impurities in the Ta2O5 layer.
Curing a Ta2O5 layer by a low temperature oxidation annealing process can be performed using O3 or UV-O3. The curing mechanism can be as follows: O3 is separated into O2 and O (single oxygen atoms), using UV radiation. The separated single oxygen atoms can penetrate the Ta2O5 layer and attach to a dangling Ta bond site. In a high temperature UV-O3 annealing process, the curing effect of the O3 can be reduced while the curing due to thermal effects can be increased. Since the object of the low temperature oxidation annealing process using O3 or UV-O3 may be to improve the leakage current characteristics in a capacitor employing a Ta2O5 layer, it may be preferable for the process to be performed within an appropriate range of low temperatures.
It is known that the Ta2O5 layer can be crystallized by exposure to temperatures of about 720xc2x0 C. Thus, it may be preferable that a high temperature heating process for crystallizing the Ta2O5 layer is performed at a temperature higher than 720xc2x0 C.
When the annealing process using UV-O3 is performed at a temperature higher than the crystallization temperature of a Ta2O5 layer, excess oxidation can occur between the Ta2O5 layer and a lower electrode, and electrostatic capacity of the layer may be reduced to one half or less of its original value. Thus, in order to suppress the excess oxidation and promote the curing effect of the O3, the annealing process by UV-O3 can be performed at a temperature that is lower than the crystallization temperature of the Ta2O5 layer, and the crystallization of the Ta2O5 layer can be performed at a temperature that is higher than or equal to the crystallization temperature of the Ta2O5 layer.
Conventional single wafer machines may use a resistance heater (the heater). Changing the temperature of the wafer using the heater may, however, take considerable time which could increase the fabrication time for the wafer. For example, in order to perform the low temperature oxidation annealing process and the high temperature heating process on the Ta2O5 layer using the same heater, the heater temperature is maintained at an appropriate temperature for the low temperature oxidation annealing process of the Ta2O5 layer, for example  less than 500xc2x0 C. Then, the heater temperature is increased to increase the temperature of the wafer to a temperature that is greater than or equal to the crystallization temperature (720xc2x0 C.) to perform the high temperature heating process. The time needed to change the temperature of wafer from the low temperature oxidation process to the crystallization process temperature may take several tens of minutes.
It is known to perform the low temperature oxidation annealing process and the crystallization process using different wafer machines. For example, the low temperature oxidation annealing process can be performed in a wafer type apparatus using a resistance heater, and the high temperature crystallization process can be performed by dry O2 annealing using a separate furnace type apparatus.
Using a separate furnace to perform the high temperature crystallization process may take thirty minutes to an hour. Moreover, if the time needed for increasing and lowering the temperature before and after crystallizing the Ta2O5 layer is added, it may take over four hours to perform the high temperature crystallization processing. Thus, the thermal budget may be increased while reducing wafer throughput. The complexity of the fabrication process may also be increased.
Embodiments according to the present invention can provide methods for forming capacitors including Ta2O5 dielectric layers including changing a wafer to heater separation or process chamber pressure. Pursuant to these embodiments, a Ta2O5 layer can be maintained at a first temperature that is less than a temperature for crystallization of the Ta2O5 layer. At least one of a position of the Ta2O5 layer in the process chamber relative to the heater and a pressure in the process chamber is changed to increase the temperature of the Ta2O5 layer to about the temperature for crystallization.
In some embodiments according to the present invention, the Ta2O5 layer in the process chamber is in a first position in the process chamber that is separated from the heater by a first distance. The Ta2O5 layer is moved from the first position to a second position in the process chamber that is separated from the heater by a second distance that is less than the first distance. In some embodiments according to the present invention, the first distance is about 2 mm and the second distance is less than about 1 mm.
In some embodiments according to the present invention, the Ta2O5 layer is in a first position in the process chamber that is separated from the heater by a first distance. The Ta2O5 layer is moved from the first position to a second position in the chamber that is separated from the heater by a second distance that is greater than the first distance. The Ta2O5 layer is moved from the second position to a third position in the chamber that is separated from the heater by a third distance that is less than the first distance.
In some embodiments according to the present invention, the heating further includes heating the Ta2O5 layer to a temperature that is less than about 650xc2x0 C. in an O3 or UV-O3 atmosphere in the process chamber. In some embodiments, the changing further includes heating the Ta2O5 layer to a temperature that is greater than about 750xc2x0 C. in an O2, N2O, N2, Ar, or He atmosphere.
In some embodiments according to the present invention, the changing includes increasing the pressure in the process chamber to increase the temperature of the Ta2O5 layer to about the temperature for crystallization. In some embodiments according to the present invention, the first pressure is about 1.0 Torr and the second pressure is about 300 Torr.
In some embodiments according to the present invention, the Ta2O5 layer is in a first position in the process chamber that is separated from the heater by a first distance. The Ta2O5 layer is moved from the first position to a second position in the chamber that is separated from the heater by a second distance that is less than the first distance and the first pressure is increased to the second pressure in the process chamber.
In some embodiments according to the present invention, the heating further includes moving the Ta2O5 layer to a second position in the chamber that is separated from the heater by a first distance and moving the Ta2O5 layer away from the heater as the temperature at the first position is increased.